1. Field of the Invention
The present invention relates to a mutually authenticating method, a program, a recording medium, a signal processing system, a reproducing apparatus, and an information processing apparatus that cause a drive connected to for example a personal computer to record an encrypted content to a disc medium and to reproduce an encrypted content from a disc medium.
2. Background Art
On one recording medium such as a DVD (Digital Versatile Disc), which has been recently developed, a large capacity of data for one movie can be recorded as digital information. When video information and so forth can be recorded as digital information, it will become important to protect copyright of digital information against illegal copies.
In DVD-Video, as a copy protection technology, CSS (Content Scrambling System) has been employed. The use of the CSS is permitted for only DVD-ROM media, not recordable DVDs such as a DVD−R, a DVD−RW, a DVD+R, a DVD+RW, and so forth due to CSS contract. Thus, the CSS contract does not permit the user to copy the contents of a DVD-Video disc that has been copyright-protected in accordance with the CSS system to a recordable DVD (so-called bit-by-bit copy).
However, there was a serious situation of which the CSS encrypting system was broken. Illegal software called “DeCSS” that is capable of easily decrypting contents that has been encrypted in accordance with the CSS encryption system and copying the decrypted contents to a hard disk was published on the Internet. As a background of the advent of “DeCSS”, reproduction software was designed with a CSS decryption key that was not anti-tampered although it was supposed to be anti-tampered. The reproduction software was reverse-engineered and the encryption key was decrypted. As a result, all the CSS algorithm was decrypted.
As a successor of the CSS, CPPM (Content Protection for Pre-Recorded Media) as a copyright protection technology for DVD-ROMs such as a DVD-Audio disc and CPRM (Content Protection for Recordable Media) as a copyright protection technology for recordable DVDs and memory cards have been proposed. In these systems, even if there is a problem about encryption for contents, storage of management information, and so forth, the systems can be updated. Even if data of a whole disc is copied, the reproduction can be restricted. A method for protecting copyright for DVDs is described in the following non-patent related art reference 1. The CPRM is described in the following document distributed by its licenser, 4C Entity, LLC, USA.
“Spreading-out Copyright Protection Space Starting from DVD”, Yamada, Nikkei Electronics, pp. 143-153, 2001.8.13.
“Content Protection for Recordable Media Specification DVD Book”, Internet <URL: http://www.4Centrity.com/>
In a personal computer (hereinafter, sometimes abbreviated as PC) environment, since a PC and a drive are connected with a standard interface, secret data may be leaked out or tampered at the standard interface. As a result, there is a risk of which application software may be reverse-engineered and secret information may be stolen or tampered. Such a risk hardly occurs in an electronic apparatus that has a recording and reproducing apparatus that is integrated thereinto.
When a copyright protection technology is implemented to an application program that is executed on a PC, to prevent the copyright protection technology from being analyzed, the application program is generally anti-tampered. However, there is no index that represents the strength of tamper-resistance. As a result, countermeasures against reverse-engineering depend on the decision and capability of each implementer. Thus, the CSS was broken. The copyright protecting technologies CPPM and CPRM for recordable DVDs, which were proposed as a successor of the CSS are based on the known CSS and have new additional functions. In addition, most of algorithms of copyright protection technologies depend on implementation to a PC. Thus, it cannot be said that they have strong content protection functions. In other words, an encrypting system would be broken by analyzing secret information of a copyright protection technology for example reverse-engineering using application software. Encrypted content read as data from a disc by a PC would be decrypted by decrypting software such as “DeCSS”. The decrypted data would be repeatedly copied as a clear content in non-copy-protection state. Thus, there was a risk of which the copyright protection would not work.